Searching \ for '[EE] Good general purpose voltage reference' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power.htm?key=voltage
Search entire site for: 'Good general purpose voltage reference'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Good general purpose voltage reference'
2004\11\17@042916 by Glenn Jones

picon face
Hello,
I am looking for suggestions for a good reliable general purpose
voltage reference chip. The voltage I need eventually is 2.5 V, but I
could divide down from 4.096 or the like. The system has a 5V supply.
I don't need anything too accurate, +-.01V would be good. If possible,
I'd like something that has been around a while so that I can hope
that it will be available for 10-20 years, or at least a pin
compatible replacement. Is there a standard voltage reference pinout?
Temperature stability is also important, but I'm not sure exactly how
much so. Is 100 ppm/deg C unreasonable?
Thanks for any advice,
Glenn
____________________________________________

2004\11\17@045108 by hael Rigby-Jones

picon face


{Quote hidden}

Virtualy all references meet or better 100ppm. If you want to pay for it you
can get better than 2ppm references.  However, I guess we'll need some more
requirements before suggesting parts.  Do you want through hole or surface
mount parts?  What current capability do you need? (The PIC's A/D can take
quite large currents from the reference).  I cost a big issue?

Regards

Mike

=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
____________________________________________

2004\11\17@045605 by Attila Muhi

flavicon
face
National Semiconductor LM385-2.5 ???


Regards

Attila - SM4RAN

______________________________________________________

Gratis visitkort - klicka här !
Allt inom e-handel! http://www.torget.se


-----Ursprungligt meddelande-----
Från: Glenn Jones <.....lynxlabKILLspamspam.....gmail.com>
Till: EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu <piclistspamspam_OUTmit.edu>
Datum: den 17 november 2004 10:46
Ämne: [EE] Good general purpose voltage reference


{Quote hidden}

>____________________________________________

2004\11\17@054636 by Glenn Jones

picon face
Hello,
Thank you for the reply.
I have no preference for through hole vs. surface mount. I do not
expect any large current capability from the reference, I intend to
buffer it with an op-amp, but if there are references out there that
can supply 10 - 50 mA, that'd be great.
Thanks,
Glenn


On Wed, 17 Nov 2004 09:55:29 -0000, Michael Rigby-Jones
<@spam@michael.rigby-jonesKILLspamspambookham.com> wrote:
>
>
>
>
> >{Original Message removed}

2004\11\17@074037 by Mohit Mahajan
flavicon
face
National's:
LM136-2.5/LM236-2.5/LM336-2.5V.
Operating current of 400 µA to 10 mA
Long Term Stability: 20 ppm

Regards,
Mohit.

> {Original Message removed}

2004\11\17@080630 by hael Rigby-Jones

picon face
{Quote hidden}

Firstly be carefull when buffering, the input offset of an op-amp can easily
have a worse tempco than your voltage reference.

Have a look at the Linear Technology LT1461
(www.linear.com/pc/productDetail.do?navId=H0,C1,C1154,C1002,C1243,P20
76 ).  This is availble with 2.5volt output and can source up to 50mA,
tempco 3ppm.  Not cheap though, $1.95 in single quantities for the cheapest
variant.

Analog Devices make the RE192 (
http://www.analog-devices.com/en/prod/0,,769_838_REF192%2C00.html ). Tempco
5ppm, output current 30mA, cost $1.24/1000

Unfortunately the high output current, low tempco and low cost reference
doesn't seem to exist IME, but I'd be happy to learn otherwise!

Mike


=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
____________________________________________

2004\11\17@080722 by olin_piclist

face picon face
Glenn Jones wrote:
> I am looking for suggestions for a good reliable general purpose
> voltage reference chip. The voltage I need eventually is 2.5 V, but I
> could divide down from 4.096 or the like. The system has a 5V supply.
> I don't need anything too accurate, +-.01V would be good.

That's .4%, which is actually quite accurate.  There are lots of choices at
1% and 2%, but less than .5% will limit the field considerably.

> Temperature stability is also important, but I'm not sure exactly how
> much so. Is 100 ppm/deg C unreasonable?

No, that's quite a bit.  Note however that a 40degC variation blows your
entire error budget.  For example, if you can only guarantee the temperature
stays within a 20degC range, then you need .2% initial accuracy.  That's
going to be expensive.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\11\17@081140 by olin_piclist

face picon face
Glenn Jones wrote:
> I have no preference for through hole vs. surface mount. I do not
> expect any large current capability from the reference, I intend to
> buffer it with an op-amp, but if there are references out there that
> can supply 10 - 50 mA, that'd be great.

First, 50mA is "large" current for a voltage reference.  Second, buffering
with an opamp is going to introduce additional errors.  You wanted the
result to be 2.5V within 10mV.  The opamp will eat up a millivolt or two due
to its offset voltage.

You should step back and explain the overall problem.  You seem to have
jumped into the middle specifying something without understanding the
tradeoffs and what's out there.  It sure sounds like this problem needs to
be solved with a more global look at the circuit.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\11\17@094912 by Spehro Pefhany

picon face
At 01:29 AM 11/17/2004 -0800, you wrote:
>Hello,
>I am looking for suggestions for a good reliable general purpose
>voltage reference chip. The voltage I need eventually is 2.5 V, but I
>could divide down from 4.096 or the like. The system has a 5V supply.
>I don't need anything too accurate, +-.01V would be good. If possible,
>I'd like something that has been around a while so that I can hope
>that it will be available for 10-20 years, or at least a pin
>compatible replacement. Is there a standard voltage reference pinout?
>Temperature stability is also important, but I'm not sure exactly how
>much so. Is 100 ppm/deg C unreasonable?
>Thanks for any advice,
>Glenn

Hi, Glenn:-

Here are some general suggestions, but there are lots of other
possibilities depending on the exact requirements. Note that if you
use another voltage and divide it down or buffer it you'll need to
consider resistor errors and drift or offset voltage etc. in the
error budget. Buffering for the PIC ADC reference requires a very
low impedance source; probably a bit more than a simple op-amp output,
like a couple of resistors and a cap to get a stable low-Z source.

LM4120AIM5-2.5 +/-0.2% initial accuracy +/-50ppm/K series voltage reference.
$1.00 1K / 1.62/100   160uA typical draw (has 2uA shutdown)

LM4040BIM3-2.5 +/-0.2% initial accuracy +/- 100ppm/K shunt voltage reference
$0.62 1K / 0.87/100   (needs about 100uA to operate)

LM431CCZ  +0.5%/-0.6% initial accuracy +/-50ppm/K shunt voltage reference
$0.33 1K/ 0.51/100  (needs about 1mA to operate)

The LM431 is made in enormous volume by many suppliers, but most versions
are only +/-1% accurate, and it needs about 1mA to regulate. The lower
accuracy versions get down to the 10-cent range in medium volume.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffEraseMEspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




____________________________________________

2004\11\17@102907 by olin_piclist

face picon face
Spehro Pefhany wrote:
> Here are some general suggestions, but there are lots of other
> possibilities depending on the exact requirements. Note that if you
> use another voltage and divide it down or buffer it you'll need to
> consider resistor errors and drift or offset voltage etc. in the
> error budget. Buffering for the PIC ADC reference requires a very
> low impedance source; probably a bit more than a simple op-amp output,
> like a couple of resistors and a cap to get a stable low-Z source.

Or you can feed the 2.5V reference into the A/D as another input, run the
A/D reference off the Vdd supply, and do the correction in firmware.  This
is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
to an A/D input.  The reference voltage is still read with about 1 part in
500 resolution, which is well beyond its accuracy.  Multiplying it up to a
higher voltage would have introduced much more error than it would have
given back in terms of A/D resolution.  Correcting the other readings to the
measured reference is just a little math in the firmware, which costs
nothing in parts and introduces virtually no additional error.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\11\17@125709 by Herbert Graf

flavicon
face
On Wed, 2004-11-17 at 10:29 -0500, Olin Lathrop wrote:
> Or you can feed the 2.5V reference into the A/D as another input, run the
> A/D reference off the Vdd supply, and do the correction in firmware.  This
> is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
> to an A/D input.  The reference voltage is still read with about 1 part in
> 500 resolution, which is well beyond its accuracy.  Multiplying it up to a
> higher voltage would have introduced much more error than it would have
> given back in terms of A/D resolution.  Correcting the other readings to the
> measured reference is just a little math in the firmware, which costs
> nothing in parts and introduces virtually no additional error.

Wow, that's a really cool idea! Thanks Olin, I'll store that one for
later use. TTYL

____________________________________________

2004\11\17@161333 by Spehro Pefhany

picon face
At 10:29 AM 11/17/2004 -0500, you wrote:
>Spehro Pefhany wrote:
> > Here are some general suggestions, but there are lots of other
> > possibilities depending on the exact requirements. Note that if you
> > use another voltage and divide it down or buffer it you'll need to
> > consider resistor errors and drift or offset voltage etc. in the
> > error budget. Buffering for the PIC ADC reference requires a very
> > low impedance source; probably a bit more than a simple op-amp output,
> > like a couple of resistors and a cap to get a stable low-Z source.
>
>Or you can feed the 2.5V reference into the A/D as another input, run the
>A/D reference off the Vdd supply, and do the correction in firmware.  This
>is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
>to an A/D input.  The reference voltage is still read with about 1 part in
>500 resolution, which is well beyond its accuracy.  Multiplying it up to a
>higher voltage would have introduced much more error than it would have
>given back in terms of A/D resolution.  Correcting the other readings to the
>measured reference is just a little math in the firmware, which costs
>nothing in parts and introduces virtually no additional error.

That sounds like a good solution for that problem.

Depending on what you're doing, the resolution and quantization noise may
be very important. Worst case, without dither and digital low-pass
filtering, you could have the reference bobbling up and down a count and
the input bobbling up and down a count, which would represent a +/-0.8%
variation. Not acceptable if you're trying to display engineering units,
such as 800°F or 1000 PSI. It would also degrade the derivative term
in PID control (requiring more filtering). There are also possible issues
with Vdd variations if there are heavy loads from the Vdd bus (a device
I'm developing at the moment has a load that varies from 0 to 2A with
fairly sharp edges. It would be possible to run the micro on a separately
regulated 3.3V supply to reduce short-term variations in Vdd for the micro,
but that results in additional complexity with the mixed voltages on the board.)

Hopefully Microchip will soon figure out (like several other companies have
been doing for years) how to put proper delta-sigma ADCs (and dare I ask for
a PGA option?) into inexpensive PICs so we won't have to deal with crummy
10 bit resolution for much longer.

With a 16-24 bit ADC option, then we can really forget about resolution
issues and concentrate on accuracy.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com





___________________________________________

2004\11\17@173637 by Shawn Mulligan

flavicon
face
Excellent!

-----Original Message-----
From: RemoveMEpiclist-bouncesEraseMEspamEraseMEmit.edu [RemoveMEpiclist-bouncesspam_OUTspamKILLspammit.edu] On Behalf Of
Olin Lathrop
Sent: Wednesday, November 17, 2004 8:30 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Good general purpose voltage reference

Spehro Pefhany wrote:
> Here are some general suggestions, but there are lots of other
> possibilities depending on the exact requirements. Note that if you
> use another voltage and divide it down or buffer it you'll need to
> consider resistor errors and drift or offset voltage etc. in the
> error budget. Buffering for the PIC ADC reference requires a very
> low impedance source; probably a bit more than a simple op-amp output,
> like a couple of resistors and a cap to get a stable low-Z source.

Or you can feed the 2.5V reference into the A/D as another input, run the
A/D reference off the Vdd supply, and do the correction in firmware.  This
is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
to an A/D input.  The reference voltage is still read with about 1 part in
500 resolution, which is well beyond its accuracy.  Multiplying it up to a
higher voltage would have introduced much more error than it would have
given back in terms of A/D resolution.  Correcting the other readings to the
measured reference is just a little math in the firmware, which costs
nothing in parts and introduces virtually no additional error.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

2004\11\18@082846 by Morgan Olsson

flavicon
face
Smart solution :)
Note however that if Vdd varies dynamically only +/- 1% between A/D samplings, both the reference and interesting input converted values will vary that much, ending up in +/- 2% additional error after calculation.
/Morgan

Olin Lathrop 16:29 2004-11-17:
>Or you can feed the 2.5V reference into the A/D as another input, run the
>A/D reference off the Vdd supply, and do the correction in firmware.  This
>is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
>to an A/D input.  The reference voltage is still read with about 1 part in
>500 resolution, which is well beyond its accuracy.  Multiplying it up to a
>higher voltage would have introduced much more error than it would have
>given back in terms of A/D resolution.  Correcting the other readings to the
>measured reference is just a little math in the firmware, which costs
>nothing in parts and introduces virtually no additional error.

--
Morgan Olsson, Kivik, Sweden

____________________________________________

2004\11\18@102330 by olin_piclist

face picon face
Morgan Olsson wrote:
> Smart solution :)
> Note however that if Vdd varies dynamically only +/- 1% between A/D
> samplings, both the reference and interesting input converted values
> will vary that much, ending up in +/- 2% additional error after
> calculation.

This is true.  In my case I oversampled the signals considerably, then low
pass filtered each by 2 or 3 poles (can't remember) before doing the math to
get the corrected values.  If you need high speed, or as someone else
pointed out, have a control loop that can't tolerate some filtering, then
this is not a suitable approach.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
____________________________________________

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...